This invention relates to air-to-air heat exchangers for reclaiming energy from the air exhausted from heated or cooled buildings. The exhaust from a typical combustion furnace or other heating unit may contain on the order of one third of the energy supplied to the furnace; thus, tremendous losses of energy occur unless energy is reclaimed from the exhaust airstream. Similarly, in airtight buildings where it is desired to exhaust foul air to the ambient and pump fresh air into the building, there is a need for a more effective air-to-air heat exchanger, to reclaim more of the energy from the exhaust air.
Efforts have been made to reclaim energy from exhaust airstreams. The heat recovery wheel, as described in Energy Conservation Through Heat Recovery, published in the 1970s by Northern Natural Gas Co., passes the exhaust airstream through one half of a porous heat-absorbing wheel; incoming air is passed through the other half. The wheel slowly turns, transferring heat from the exhaust airstream to the incoming air. Such wheels tend to be very large in size and are typically used in balanced systems where the incoming airstream has the same volumetric flow rate as the exhaust airstream (e.g., the airtight building example).
When the exhaust airstream contains undesirable gases such as products of combustion, the undesirable gases have been purged from the heat recovery wheel to prevent them from being blown back into the building with the incoming air. A pie-shaped purging section at the boundary between the exhaust airstream and the incoming airstream has been employed, in combination with pie-shaped compartments in the wheel, to redirect back through the heat recovery wheel and into the outgoing exhaust incoming air that flows into the pie-shaped section.